Cavity resonator electron tube



April 26, 1949 J. H. o. HARRIES 2,468,441

CAVITY RESONATOR ELECTRON TUBES Filed Oct. l2, 1946 l 5 Sheets-Sheet l WMM 4 ATo/ewgy April 26,l 1949.. J. H. o. HARRIES 2,468,441

CAVITY RESOATOR ELECTRON TUBES Filed oct. 12, 1946 l 5 sneet-sheet 2 l .Mita/fm April 26, 1.949- J. H. o. HARRIES v 2,468,441

cAvITY RESONATOR ELEcTRoN TUBES Filed Oct. 12, 1946 4 5 ShetS-Shet 5 A T TOP/VE Y April 26, 1949! .1. H. o. HARRIS 2,468,441

CAVITY RESONATOR ELECTRON TUBES Filed Oct. l2,l 1946 5 Sheets-Sheet 4 /N l/E/V TOI? Mm m, x14/m Wal/J @1MM O 5,0 o 10.000 l/0L7'5 Vb v ATTORNEY April 26, 1949i. J. H. o. HARRIES CAVITY RESONATOR ELECTRON TUBES 5 Sheets-Sheet 5 Filed Oct. l2,4 1946 ATTORNEY Patented Apr. 26, 1949 UNITED STATES PATENT OFFICE Application October 12, 1946, Serial No. 703,013 In Great Britain November 3, 1945 19 Claims.

The present invention relates to electron beam valves and, more particularly speaking to valves furnished with an electrical cavity resonator.

In such valves, some of the energy in an electron beam is transferred to oscillatory elds in the cavity resonator. These fields constitute standing electromagnetic waves within the cavity. The proportion of the total input electron beam energy which is transformed into wave energy in this way is usually referred to as the eiciency of the valve.

To effect this transfer of energy, it is necessary to establish along the path of the beam of electrons an electric eld of certain shape, directions, and magnitudes.

As far as is known, the shapes, directions and magnitudes of the eld, actually found inside any one of known kinds of resonant cavity depart very substantially from those necessary to convert a really substantial portion of the D.C. energy of the beam into oscillatory output energy. Therefore, although electron beam valves have been proposed in which a beam of electrons has been set up and a cavity resonator employed, such known forms of valve have cavities of such a shape that the fields therein are such that the eiiiciency of conversion of input electron beam energy to oscillatory power is very low. Therefore, these valves have only a very limited usefulness. For example, a reection type of velocity modulation valve furnished with a single resonant cavity, has an eiiciency, in practice, of only the order of about or less and that of a diode furnished with a single resonant cavity is even less.

Moreover, when used at extremely short wavelengths, the cavity resonators hitherto employed are usually so small as seriously to limit the power output which the valve can handle.

One of the objects, therefore, of the present invention is to produce an electron beam valve provided with a single cavity resonator in which cavity there is an internal eld of shape, magnitude, and direction such that a comparatively high eii'iciency is produced, and a further object of the invention is to provide resonant cavities for use in such valves, which are large at a given wavelength compared with those hitherto available.

In order to make the present invention, it has been found necessary to carry out investigations to increase the knowledge available of both electrons beams and resonant cavities. These two investigations were as follows:

(a) The shape, magnitude, and direction of the oscillatory iields which are best placed in the path of a beam of electrons in order to convert the D.C. power of the beam into oscillatory output power in an efficient manner have been investigated, both mathematically and experimentally. This investigation has yielded certain information which is believed to be new, or at least, not fully appreciated or explained previously.

(b) Another investigation into the field shapes, magnitudes, and directions, which can in fact be obtained in resonant cavities for use in electron beam valves has also been carried out. In general, prior knowledge has not been such that it was possible to predetermine or calculate these eld shapes. This is because it is not practicable, in the more complex and useful cases, to solve certain basic differential equations. An experimental approach was also difficult, as it is necessary to study the magnitude and direction of the eld at all points within a large number of shapes of resonant cavity. As far as is known, no suitable measuring device, or method of doing this, has hitherto been known.

By means of a new method of measurement and new measuring devices partly described below, it has been possible to devise a new shape of cavity resonator having fields of new shapes, magnitudes, and directions. This new shape of cavity has certain unique features, and is especially useful in electron beam valves, and inter alia forms part of the present invention.

By building, therefore, upon the results of both these investigations, the present invention has been made and according to the invention an electron beam valve is furnished with a resonator in which there are an input sub-cavity, a main sub-cavity and an output sub-cavity, abutting in that order one upon the other, the input and main sub-cavities being separated by an input septum, and the main and output sub-cavities being separated by an output septum; the outside wall of the input sub-cavity is formed with a beam entrance aperture across an axis which is common to the three sub-cavities while the input septum is substantially complete except for a substantially parallel-sided deflection slot lying across the said axis; the output septum is also substantially complete except for the provision of a substantially parallel-sided slot lying across the said axis, and a grid is placed alongside that slot; the deiiection slot and the slot in the output septum are parallel; the cathode and beam forming means are arranged so that the electron beam when produced will pass through the beam entrance aperture, along the axis into the input sub-cavity and onto the deflector slot so that for at least one mode of resonance of the resonator an alternating electric eld transverse to the axis exists across the deection slot and an output electric eld substantially parallel to the axis exists in the output sub-cavity between the said grid and the opposite wall of the output cavity and the `eld in', the'gre'ater partof the main subcavity is of less 'magnitude than either of these latter elds.

A pair of grids may be provided on either side of the slot in the output septum. =The;axis=need not be in the centre of thepsub-cavities.

The grid may be provided-l with yone aper-v ture or many of circular, rectangularforwother shapes.

Again, a part of the outside wall of the output cavity is conveniently arranged to'project towards the output septum opposite the area of ,fthatse'ptumf wherefthe gridor.grids are placed.

vThe relative dimensions-mf f the. input -output'sube-cavities 'may be such that 'at at# leastvone 'fmodeof resonance .of theresonant-"cavity,ian -electricfieldtransverseto'the axis exists across ...'the'fdeflection slot fandwou'tputelectric elds substantially parallelutovthe 4axisfexist in therout- -put sub-cavity ".'oppositem the grid or, grids, the ratio between the magnitude of the transverse electric held` and fthe.; magnitude of fthe outputeA .electric fleldbeinglsuchthatat some yworlirigfipo- .'-tential uponthe resonant cavity; with respect-...to

the cathode, vzand-iwl1en the saidf=electronP beam .srenters theicavity, continuousoscillations are. gen- Y erated.

In order .thatthe inventionmay be clearly .understoodfvand readilymcarriedffinto effect, `some exam-ples or particular-forms. of-constructi`0n of the invention 4Willi nowI be; lmore =fully- 'described with lreference..-- to the lfaccompanyng f drawings, tiny which:

Figure l is vran. explanatory 'diagram of i yelectric` elds;

Figure 2 is an axial section' fof. a'complete .valve iinraccordancetwith itheiV invention;

Figure 3.- -is 'af-perspective view .of4 the 'left-hand halfof thefca'vity resonator "shown'z-in Fig. '2;

"Figure 4 is; an:y exploded'viewfofl the f pressings :used 2to makefup' their-cavity resonatorfsh'own. in

Fig.'

' ^Figure 5 is a curve v`or fgraphs'fusedin the' -vdesign of the structure;

' Figure 162 is a: diagrammatic:y axial section-Lof a woodeni'model' ;off rhalf ithe cavity Vresonator :cov- :ered .with copper fsheet.fandsused` in. testingthe 3, L design;

' Figures .7and 81 show-twolmore explanatory --curves'lor graphs;

' Figure Sis aperspectivefview of fan-'alternative f' form of cavity resonator TofA squaref shape;

Figure 10 isla section of-a somewhat modi- `V`ed Ar form4 .of y cavity resonator;

yFigurell `is a sectionfiofwanother modification :with the' back grids valtoge'tl'ier omitted; Figure 12 :is a iside elevation .and

lonators with a` waveguide-leading 'ofi from `one side; while Figure 14 isa dia'gramfof a-cavity4 resonator to: illustrate I modes "of application of lthe fvinven- I 7 resonance lat which" ther Figure 13: isf. aplan Lofa1nlumber-off'cavity respose, the beam enters the field system at a velocity vox in the 0.7: direction, and passes first through an 01u-directed or transverse input oscillatory eld 2. This eld 2 causes the beam to be deflected transversely in an oscillatory manner between the two positions 3 and 4 shown by the dotted lines. The beam travels across a eldfree space 5v-and is deected alternately into two fioutput' eldsv 62.11, which are' in opposite phase or pushp'ull and 'are oscillatory at the same frelquency as the input field 2. In the course of the investigation (a) mentioned above, it was found mithatathe -energyfrevzluired to deflect the electron beam as shown in Fig. 1 is very small compared A15 withthelpower vvcarried by the electron beam. If

f thelectron beamrenters the oscillatory output =.eelectric.fields4 6, 'l at an appropriate phase compared with the input field 2, and if the magnivf-itfudefof these elds is appropriate then a substantial portion of thelelectron beam energy will lebe;` transferredtofthe-=oiitpi1tl rfields .6,- 1. f The-dif- 4rfe'rence inf fphase between fthefinput 'l'eld' 2-A y'and ther-output' eldse 6, 'l wilt ibei determined by" the l stransit timet ofrtheiaelectrons betweenithe 4:input f A Yfree spacez-5- fbetweenithem. If,moreover-,: alll the elds n l, 6' :fand 'learef partf'ofl-thef-samezieldfsysstern,E some1-of thesenergyfideliveredfto the 'output fields/Egt1,.:byf'therfelectron beam I ".will fappear-iin ,f the` input- "'iieldei 2 :Handi if ythe I .above-,mentioned phase is suitable and suiicient .energyV is delivered rsby the'i beam I,f,;a regenerativer effect .will .take pla-ceafandt the i'systemzsas. ai wholecan generate .c'ontinuous..ioscillations.

Such a field system.is-iusedf-inilelectron beam values; in accordance with,.fthe`fpresent invention. "InrEig 2 .the:` cross -secti'on-Jof a" cavity'lresonator -1'llinatieuirr Vaccordance."with:the' "present :invention is shown. diagrammaticallyrasiwell as lan :electron 4QA beam I. which= isI representeddiagrarnmatically as '-fli-avingfibeenf produced by xian` electron f @gunfvvof "Lknownvtypeicomprisingalstraightwcathodef and shieldr-'l at ori near-cathode potential. The elec- Jtron f'beam .'theritravels through affslot il imV in'I a fbeam` torming :pressing 326,v into the resonator .f through Iian:fentranceis'lot I l'. 'fThe'Y shape rofi the wresonatorzt` is, maccordance withithe present in- -wventongzsuch that thef electronE beam.: l therein -passes :Sthrou'ghl' andino-operates' with ian oseily.50 :laitory lfield systemisuch Easc that explainedf with and then through an outlet slot |2a. -Whenithe ffb'eam isrdeflected; i it passes "a'lternatelyf'through twofpairslbf -gridstfyl @2g-.fand g3; gib-and` 'finally strikes aback-'plate -I-3.

Inv lorderflto `faccelere/telfthebeam 'throughjl the f/.entrance-"slotl ll nfthis armer-fthe resonators is lfmaintainedLby -ttery, r?? the"` like V(notishown), `at apositivepotential'Vswithf-respect totheca'tho'de; .applied .toa terminalftll.

Such a fresonantf-fcavi-tylf f possesses -a f mode lof xistsmanfintense oscilllatoryelectrieldacros `.the "slot f l2 g l which" elcl fisf/ transverse to the initial1 entran-ce directionffof theellectroriibeam i l. The electric lfield fin "the space 5 is much weaker than that in the slotCI'Z, ofbutisfialso fr'substantially: itransverse toftheienzztrancefdirectiorrofthefelctronbeam. fTliereal'so -Jex-ist two outputfeldsoini the?. gaps 211.5; f i6, respec- .itivelyfbetween: the'palrotfgrids gl; fg andthepair of grids g3, g4, so .thatthe'i eleetrorrfbeaml--is 'verse eld at the slot I2. These two output elds at the gaps I5, I6 haye directions substantially parallel to the entrance direction of the electron beam at the entrance slot I I, and are 180 degrees out of phase with each other, that is to say, they are in pushpull. The electron beam I after passing through the pairs of grids gl, g2, and g3, g4, impinges upon the back plate I3; the space I'I between this back plate I3 and the nearest grids g2 and g4, being substantially free of eld.

The system shown in Fig. 2 will be recognized as providing oscillatory electric elds Within the cavity resonator 8 which are closely equivalent, and in fact operate similarly, with respect to the 4 electron beam I, as' the ields 2, 6 and 1 in Fig. 1

operate with the electron beam I in that figure.

As explained with reference to Fig. 1, the electric iields in the cavity resonator 8 in Fig. 2 are part of the same system, and energy delivered from the electron beam I to the output elds in the spaces I5, I6 will appear in the input deflection field in the slot I2. If the phase relation between the deiiections at the slot I2 and at the output fields at I and I6 is appropriate, and the losses of the system are not too great, then the beam I will be set into continuous tranverse oscillation, and the system will generate oscillatory energy.

' transit angle which determines the phase relation abovementioned will be principally proportional to the distance :c2 in Fig. 2, and inversely proportional to the square root of the potential Vb at which the resonator is maintained with respect to the cathode 9 and to the mode and wavelength at which the resonator 8 is operated.

It will also be necessary for the magnitude of the transverse input field in the slot I2 to bear an appropriate ratio to the magnitude of the output elds in the spaces I5, I6. Therefore if Ey is the maximum instantaneous value of the maximum transverse input eld in the slot I2 and Ex is the maximum instantaneous value of a maximum iield in the path of the electron beam I in the spaces I5, I6, an important parameter will be the ratio K:Eg/Ex.

It will be observed that the resonant cavity 8 in Fig. 2 consists of three sub-cavities which will A'be referred to respectively as the input sub-cavity Aonators constructed according to the invention,

the ratio K is adjustable in a smooth and continuous manner by adjusting the relative dimensions of the sub-'cavities I9 and 20. K Will Ibe recognised as somewhat equivalent to a Acontrol of regeneration, and may be adjusted if required so that continuous oscillations are produced. In

this manner, a proper control of the oscillations and load characteristics of the electron beam valve in accordance with the invention is obtained.

It will be realised that electrons in the beam I,

in passing through ,the grids gI, g2, and g3, g4 in Fig. 2.will produce secondary electrons, and that "'pantograph type of engraving machine.

necessary the copper pressings may be held by pressings together.

unless the well known deleterious eiect of these secondary electrons is eliminated, their presence may cause a serious loss of efficiency.

In the copending patent application Serial No. 637,194, filed December 26, 1945, a method of preventing the deleterious eiect of secondary electrons is described, consisting briefly of setting the distance d in Fig. 2 (with respect to Equation A In this equation f is the frequency corresponding to the wavelength i. Thus, as set forth in said copending application, the transit angle gb may be from 0.251r radians to 0.81r radians. To assist` this suppression of seconary electrons, the grids gI, g2, g3, g4, and the backing plate I3, may also be roughened and coated with colloidal graphite. The present invention may therefore be combined in this way with the invention set forth in the said co-pending patent application.

Alternatively it may be found convenientl in some cases to use other known methods `of sup pressing secondary electrons.

In the arrangement shown in Fig. 2, the backing plate I3 may be removed, and the electrons vin the beam I after passing through the pairs of grids gl g2, g3, g4, may be collected in a bucket or like electrode (not shown) which should be of low enough potential to waste as little energy as possible.

The cavity resonator in accordance with the invention may conveniently be manufactured of copper pressings shown separated in Fig. 4 and which are welded together by mounting them on -a jig in a vacuum with silver foil interleaved between them and heating them by means of an eddy current furnace, until the silver foil placed between the pressings is melted and welds the As shown in Figure 4, the main sub-cavity 8 is formed of two cup-like ele- -ments joined together in axial alignment with their open ends in abutting relation, and the 'input and output sub-cavities I9 and 2| are formed respectively of cup-like elements of smaller size arranged in axial alignment with cups 29 and 30 and having their open ends joined respectively to the outside faces of the bottom walls of cups 29 and 30. The various slots, apertures and grids may be cut from a master template by a Where wax to a. brass backing plate during this process. Fig. 2 shows a section of a resonator constructed in this way. It is shown in greater detail in Figs. 3 and 4.

Figure 3 shows diagrammatically the beam I when undeflected, and a half-section in perspective of the cavity resonator 8 illustrated in Fig. 2, together with the nomenclature of certain important dimensions of the resonator.

The beam entrance slot I I is 1.7 mm. X 5.5 mm. long. Its length must not be so great that appreciableradio frequency energy is radiated through it when the resonator is in operation. The electron beam I is preferably arranged (by suitable known design of the electron gun 9, I0, Fig. 2

v(not shown in Fig. 3)) to have its narrowest divmension (preferably the crossover point of the 9 the field integral of Ea: across the distance d in the spaces l5, I6 between the two pairs of grids gl, g2 and g3, g4 should be about equal to the positive voltage Vb applied to the resonator with respect to the cathode. Therefore where d is the distance so marked in Figs. 2 and 3.

The amount yx by which the electron beam is deflected from the plane of symmetry of the resonator towards either of the pairs of grids gl, g2 or g3, g4 will be proportional to the shape of the transverse electric eld along the plane of symmetry of the resonator, upon which plane the entrance direction of the beam of electrons lies. This plot of transverse electric field may be made on the model resonator as shown in Fig. 6, and if desired the deection of a: may be approximately calculated by known methods of graphical integration of this eld having regard to the wavelength of operation and the potential Vb.

Fig. 6 shows a section of the resonator model. The copper plate previously mentioned covers the plane of symmetry 45. The transverse electric field E on this plane is plotted (as shown) in terms of Ex, that is, the ordinates of the curve in Figure 6 are in terms of the ratio E/EX. The boundary of a typical undeflected electron beam is shown by the dotted line I and its narrowest point by 46. The scale along the plane of symmetry 45 is divided into inches in the model, which is the equivalent to millimeters in the actual working resonator.

In further explanation, Fig. 7 shows a typical graph of transverse eld E along the distance :cH-:v2 on the plane of symmetry such as that shown in Fig. 6, the iield being plotted in terms of Ey, that is, the ordinates of the curve of Figure 7 are in terms of the ratio E/Ey.

Fig. 8 shows a plot of the approximate deflection in centimetres at the grids of the resonator as a function of Vb for K=1.

Instead of the sub-cavities being of cylindrical conguration as in Figs. 2. 3, 4 and 6, they may be of rectangular or other shape. A rectangular shape is illustrated diagrammatically in Fig. 9 as a half of the resonator divided along the plane of symmetry. Corresponding reference numerals to those employed in Fig. 3 are used and the construction can be easily followed by comparison with that iigure.

Whilst the preferred shape of resonators is that already illustrated, the re-entrant portion 4'! in Figs. 3 and 9 may be omitted. The distance :lf3 may then equal d, and the grids g2 and g4 (Fig. 2) left as before. Such a modified shape is shown diagrammatically in section in Fig. 10. The axis of the undeilected beam is indicated by the dotted line 48.

According to a further modification, after passing through the grids g2 and g4 in the output septum G8 in Figs, 2, 3, 8 etc. the electrons may be caught by a backing plate (not shown) or by a low potential bucket.

Fig. 1l shows a further modication according to which the grids g2 and g4 are omitted alto gether. This modification may also be applied to the resonators of the kind illustrated in Figs. 2,-

3, 4, 6 and 9. In general, however, the power output efficiency will be less when using this modification than when all four grids gl, g2, g3, g4 are used.

Resonant cavities in accordance with the invention, and particularly those of square coniiguration such as Fig. 9, may be mounted together and coupled tightly to each other by intercoupling slots in walls common to both cavities so as to.

operate additively as regards power output and in conjunction with a'common cathode assembly. In Fig. l2, the resonant cavities 8a, 8b, 8c, are coupled by slots (not shown) in this manner and are arranged by means of a further slot (not shown) to feed their radio frequency energy into a Wave guide 49, with a Zero potential shield la in which slots 50 are provided, so that three beams of electrons (not shown) pass through these slots into the resonators 8a, 8b and 8c, in accordance with the invention. The shield Illa is shaped in known manner in the neighbourhood of the slots 50, and

the resonators 8a, 6b and Sc,'are correspondingly I shaped in Fig. 11 at 5l opposite the slots 5l) so l that the beams of electron are shaped in accordance with the present invention.

The three cavity resonators 8a, 8b, 8c, can

therefore be set into oscillation simultaneously and radio frequency power will be delivered by all three together into the wave guide 49, down which the power may be led to a load (not shown).

Fig. 14 shows a cavity resonator 8 as in Fig, 2, with an electron gun 9b, lb, and a beam of elec trons l which is shown undeflected. A probe` electrode 52 is arranged so that the electrons in the beam l induce a current in the probe 52 which is proportional to the position of the beam i. The current to this probe is led to a controlling means 53, which is operated thereby in accordance with the amplitude of the oscillations of the electron beam I. Potentials from the 'controlling means 53 may be fed back by means of the line 54 shown in dotted lines to the electron gun 9b, 10b, so as to modify the potential of one or more of the electrodes therein. As will be appreciated, the amplitude of the oscillations produced by the Vbeam l in the resonator 8 may be controlled in propor-f' tion to the potentials applied to one or more of the electrodes of such an electron gun 9b, lill).

By this means, the power output of the device may be stabilsed and controlled.

Alternatively, the output from the controlv It will be realised that the present inventi'on may be employed not only for the generation of oscillations but for the detection of oscillations and for the reception, as well as for the trans--v mission, of electromagnetic waves.

' The control of regeneration by the magnitude of K may be used for :many known purposes. The output from the probe 52 in Fig. 14 may be employed for detection purposes, the degree The cathode 9a is provided 1li otveregenerationr 'being ;then` `preferably rfsuchfasr notl'to set theV valve into foscillation. f

The resonator shape i shown @may -ibez modified:I in detail, but if d1, d2 or d are made toofsmallgr dilicu'lties may be'foundvinobtaining-r theidesired 5 e'lfd shapestin a suitable manner; Anyvapertures'i intzthetsepta' 22,123'J-(1 "igs'..- 2,- 3,'and 9);; should,n not:'.'bei=so.: large` as to destroy-ther shielding rofl#- theses-walls.:

I claim:

1. l In; ian '.:electron'l discharge. device,- :the'\l come` bination of' a `,hollow fresonator' rhavinglan input?. su'becavityl andifa main '.'subecavityf separated '."iby-zf anfinput *septumiiand an loutput subl'cavit'yf ysep rated "fromr the main2 sublcavity byl an.v outputuils septum; the input andr voutput sub-cavities;-bei-ng'.` substantially smallerin transverse areafand in* axial .dimension-than: the main sub-cavity; the" outsidev walllof the input sub-cavity havinganelectronbeameentrance aperture formed therein; 2o'- an electron 'guni positioned -to direct an' 'electron Y beanithrough said Aaperture valong-'1an r`axis' di!- rected through said inputandv output septal,l the input septum havingan elongated defiectionfslot formedn th'erein across said axis, the'- output Isep# 25 tum having an elo'ngatedilslot formed therein" aorosssaid aXisand -parallelito said'fder'lection slot; and a portion-offsaid output septum adjacent* the" slot therein? being apertured thereby forming a grid' element.

2. An==electron discharge device 'according to" claim`^1 in Whichthe--de'flction' slot-'fand the-slot in'fth'e output septumextendentirely'facross the" input and output"sublcavitiesrespectively.

3. electron discharge device faccording'-to1 c1a2in'1`v`2 Yin'fwhich apart offithoutsidefwall off" the output sub-cavityifopposite the areaVr ofthe gr-id`=-portion of Athe output fseptuin '-is fo'rme'd y"asf a -re=entraa\;nt portion proj ectig :towards the' foute put-septum? 4. electron 'I dischargel device accordingl` to* claim 13 in which'portions of the output"septlim onfopposite sides'lv 'ofi the 'slot thereinl are 'perforated`-" thereby forming vra pair off-grid elements. I

5. velectrondischargefdevice -accordirigL-to il clain'i''4 in whichsaidtireeentrant'portion of thev` outsidewall oftheioutput sub`cavity`v is provided withan' elongated slotin alignment'ftvith-'th" slots" in said i septa; and "said "re-entrant portion beinglapertu'red*Torroppositesidesroffv the slot 50 therein thereby forming'va second"pairpffgridi elements -inali'gn-mentifwithi the lpairfvoffgrid elements fin the output' septum.

6. An electron discharge device"accordingfftot claim-5 'in' whichthe electron beamproduced by 551' said electr-'on gun 'has its i minimum 'widtli-1 near-"-Y` thuepoint'atA Which'it'passes throughthe defitio' L slotin` the' input septum,- andpasses through th'e f1 grdielern'ents in the output-septum when dei'V iieetedbyf said lde'ecztion slot.

7. An electron dischargedeviceaccordigfftof' claim :1 in'whieh'a part-ofthe outside'f'wa'll "tthe outputlsub-cavity oppositethe tarea' ioff ithi gridVv portion :ofatheioutputsepturntisfformed;asifa free entrant portion projecting towardsrthe-f output:v septum.;

8. An' electronf discharge device--.faooordingfstorv claims 7 in.v whichl .portions ot the outputI vseptu\.fn.--I on. opposite sides` of.. theslotf. thereinare. fperforated thereby forminga pair of .grid elementsn't'' 9. An electron discharge device accordingmto' claim 8 in whichfsaid re-entrant portion oftheV outside wall 'of' the output *subecavity' is provided'. with an elongatedislotl in alignment "with the" slots 'in said senta;A and *said*re-entrant'rportioni 12. being faperturedon.z'oppositeffsidescs-ofs the lslot?? threin'ffth'ereby" formingrza ssecond pair. of:f,'grid: elements.infalignmentziwith the lpair-ofgridzele ments in th'ezoutput septum: fw'

10. An `electron-';dischar'gendevice#accorclingdoo-1 :claim 1 in which the Aelectron beam produced by said electron gunlhas :i-ts. minimum width near the point at which it passes through the defiection slot in the in-put septum, and passes through/fl the grid elements in .the .output septum when deected by said deflection-slot;v

11. An electron discharge device laccording to claimal whereinofor zone fmode'v-of:fresonancenofo the resonator, the distance between the output. septumv 'andsthel inner side" ,ot` the 1 output walIf'of the':loutputtsub-cavitycorresponds toga small-Isig#v nalitranstv angle :not l'ess'tlfranaboutn0..2`51rradiaii's-I and not` greater than about 0.8'vr radi-ans rat Ithe operating frequency ofrthedevice.

12;-1An. electron-discharge `device laccordingoto` claimall in"fwhichfthedeflection slot and-the slots inthe foutput- -septumex'tend entirely` across the 3 input' and: output subecavities respectively:

13.;An'electron` discharge device according tot claim-11" in which/'a part' offthetoutsidefwalloof the :output fsubecavity: opposite the area off-fthe c: grid' portion oftheNE out put-septum isi-formed? ser a re-entrant portion projecting towards the cute; putfseptum.=

14. .Anelectron discharge\device raccord-ing ztoil claimen in-which=fportions of the output septumff onioppositersides ofi-the' slot thereinare' perforated:i therebyv forming .-a ypair' of grid elements? 15. Arrelectr'onbeam tube-rcomprising a'hollowff resonator havinganinputsubecavity andra maine` sub-.cavityy separated by anv :input f'se-ptum, .andf-'i an output fsub-cavityy separated from f rtherfmain-z subecavity-byanoutputvseptumthe -fthree -Asub e;- cavities bei-ng.aligne'dvonva common axis? andzthef. input and output sub-cavities:ioeingsubstantially;` smaller in transversearea @and fin: axial!r dimension: than the main subecavityy thezoutside :wall-:2 of-1theinput subcavityehavingaan'felectron beam. entrance? aperture:` :formedfth-erein across r-saidr. common axis; theinputfseptumfliaving' arr clon-fw gated deection slot formed: thereinlacrosse saidzf commonfaxiaf.` the outputv septum havingan elongated-slot formedfithereinf acrossfsaid'@common-'z axis and parallel to saiddeflection slot.i and: ai:

'Y portionY of- Asaid.:outputfseptu-mr'adjacent `7vthe vslot thereinabein'g fapertured thereby formingwa 'grida elementi-t 16; 1A .cavity resonator comprising ma pairxof metall-icoup-,like elementsfjoined together inaxia alignment with their :openy endsrin' 'abutting 2 rela Y tion 4to dorm.Y a A=mainfrsube'tzavityr.;y a second ipair'zf ofl -cup-like-- cien-rents Sofi smaller sizeethanfr said :2 first pair arranged in axial alignmentxwitlffsaidf rst r pairy or cups Tandr havinge their 1"open rf ends joined respectively'to' thef/outsidefffaces;V ofnthlfi bottom :walls l'-of" said-"firstz pair?i offfzcupsilto Itforrns a ypair fof fsub-'cavities :attiy opposite endsixof' saida main.A isubcavity;y fthe'f'bottomiwallsi1of: 'saidt'f1fstf pairof cups having elongatedeslotsformedthereini f in a common plane @andi extending..A throughout-` the widths of said smaller oups, one ofsfsaiidffVV smaller:v cups comprising.arrientrance' cup' having an*k entrance aperture'.formed-rJinl the? bottom fwallE thereof' in Asaid Acommon" plane, and fthe '-bottorrrv wall of the Ylargercup 'joinedtolthe other smallerAIA cup being apertured on opposite sidesfof thelo'n'f gated` fs'lo'tormed 'therein' 'thereby forming a pair of'gri'd elements.

cup having grid elements is provided with a reentrant portion in the bottom wall thereof and in alignment with said grid elements, said reentrant portion having an elongated slot formed therein in alignment with the slots in said larger cups, and said re-entrant portion being apertured on opposite sides of said slot thereby forming a second pair of grid elements aligned with said rst pair of grid elements.

18. An electron discharge device according to claim 1 and including a pickup probe mounted Within said hollow resonator in a position to be influenced by said electron beam.

19. An electron discharge device according to claim 1 in which portions of the output septum on opposite sides of the slot therein are perforated thereby forming a pair of grid elements, a part of the outside Wall of the output sub-cavity opposite the area of the grid portions of the output septum being formed as a re-entrant portion projecting towards the output septum, said reentrant portion of the outside Wall of the output sub-cavity being provided with an elongated slot REFERENCES CITED The following references are of record in the tile of this patent:

UNITED STATES PATENTS Number Name Date 2,266,428 Litton Dec, 16, 1941 2,272,165 Varian et al. Feb. 3, 1942 2,275,480 Varian et al Mar. 10, 1942 2,281,935 Hansen et al. May 5, 1942 2,407,708 Kilgore et al. Sept. 17, 1946 

